With rapid population growth and the emergence of clean energy technologies, worldwide freshwater availability is declining at alarming rates (Service, R. F. (2006) Science 313, 1088-1090). Already, 1.2 billion people do not have access to safe drinking water, with millions (mostly young children) dying annually from disease transmitted from contaminated water (Shannon, M., et al. (2008) Nature 452, 301-310; Elimelelch and Phillip (2011) Science 333, 712-717). Even developed countries such as the United States will be considered “water-stressed” before the end of the century (Service, R. F. (2006) Science 313, 1088-1090). Diminishing groundwater resources are being contaminated with increasing amounts of heavy metals, micropollutants, and reproductive toxins. Chemicals added to disinfect water supplies negatively impact the environment and often undergo side reactions that generate high levels of carcinogens in drinking water (Shannon, M., et al. (2008) Nature 452, 301-310). New technologies must be developed to treat water effectively from traditional and non-traditional sources to adequately supply global needs.
Reverse osmosis (RO) has emerged as a leading technology in water treatment for its ability to efficiently convert seawater and brackish water into high purity water for potable and high tech applications. The polymeric thin-film membranes used for RO exhibit high flux, high selectivity, low cost, and relatively low-energy expenditure compared to alternative desalination technologies (Elimelelch and Phillip (2011) Science 333, 712-717; Lee, K., et al. (2011) J. Membr. Sci. 370, 1-22). Acting as a physical barrier, RO membranes allow water molecules to permeate through a dense, microporous film and reject small dissolved solutes. Among numerous polymeric materials used to fabricate RO membranes, aromatic polyamide membranes are the most widely used because of their superior transport and separation properties. Thin-film composite membranes are produced on an industrial scale using roll-to-roll processing and are packaged into spiral wound elements to achieve optimal performance.
Although polyamide membranes have approached theoretical limits on performance, they are highly susceptible to biological surface fouling that significantly reduces intrinsic operational and economic advantages (Shannon, M., et al. (2008) Nature 452, 301-310; Elimelelch and Phillip (2011) Science 333, 712-717; Herzberg and Elimelech (2007) J. Membr. Sci. 295, 11-20). Microorganisms in the feed water adsorb onto the surface via hydrophobic interactions and block the flow of water through the membrane. Harsh chemical disinfectants used to prevent the growth of biofilms on the surface, such as chlorine and base treatments, prevent and remove biofilms from the surface but also attack the chemical bonds within the polyamide layer degrading the high selectivity of the membranes (Glater, J., et al. (1994) Desalination 95, 325-345; Kawaguchi and Tamura (1984) J. Appl. Polymer Sci. 29, 3359-3367). Thus, biogrowth inhibition and cleaning agents that are commonly used in water treatment cannot be used with RO membranes, increasing the pretreatment, operating and maintenance costs of desalination plants (Isaias, N. P. (2001) Desalination 139, 57-64; Redondo, J. A. (2001) Desalination 139, 28-31; Kang, G.-D., et al. (2007) J. Membr. Sci. 300, 165-171).
Recently, researchers have attempted to reduce or prevent RO membrane biofouling by developing anti-fouling membrane surface treatments (Rana and Matsuura (2010) Chemical Rev 110, 2448-2471; Kang and Cao (2012) Water Research 46, 584-600). By covalently modifying the surface with hydrophilic “brush” polymers (Belfer, S., et al. (1998). Membr. Sci. 139, 175-191; Van Wagner, E. M., et al. (2011) J. Membr. Sci. 367, 273-287; Kang, G., et al. (2011) Desalination 275, 252-259; Zou, L., et al. (2011) J. Membr. Sci. 369, 420-428; Lin, N. H., et al. (2010) J. Materials Chem. 29, 4642; Yang, R., et al. (2011) Chem. Materials 23, 1263-1272), hydrophobic interactions between the foulant and the membrane surface are obstructed (FIG. 1). In addition, initial attachment of biological cells and dissolved organics, a key step in biofilm formation, is impeded. Moreover, a hydrophilic surface forms a layer of hydration that prevents foulants from adsorbing onto the surface of the membrane film, thus allowing water to pass freely through the membrane.
Unfortunately, the designed chemical stability of polyamide membranes makes surface manipulations a difficult task. Previous studies have utilized reactive epoxide terminal groups (Van Wagner, E. M., et al. (2011) J. Membr. Sci. 367, 273-287), carbodiimide activation (Kang, G., et al. (2011) Desalination 275, 252-259), or radical initiated graft polymerizations that chemically attach the hydrophilic polymers to the polyamide surface (Kang and Cao (2012) Water Research 46, 584-600; Kang, G., et al. (2011) Desalination 275, 252-259; Zou, L., et al. (2011) J. Membr. Sci. 369, 420-428; Lin, N. H., et al. (2010) J. Materials Chem. 29, 4642; Yang, R., et al. (2011) Chem. Materials 23, 1263-1272). However, these modifications require long reaction times, exotic reaction conditions, and are performed in situ, preventing them from being easily translated into commercial roll-to-roll manufacturing processes for thin-film composite membranes.
Thus, there remains a need for scalable methods to produce anti-fouling RO membranes. Such membranes and methods related thereto are described herein.